When physiological or cellular fluids are administered to a patient, it is imperative that foreign particles and gas bubbles or air emboli that may be trapped in the fluids be removed. In the prior art, these fluids are passed through a filter before being administered to the patient.
One prior art filter is disclosed in U.S. Pat. No. 4,662,906. This filter includes a structure that first separates the gas from the fluid by introducing a vortex flow into the fluid. The gas bubbles that are separated from the fluid are moved into a chamber that is formed in part by a hydrophobic membrane, so that the gas exits to the atmosphere through the membrane. The fluid is then passed through a defoaming sponge, treated with an anti-foaming agent, so that any remaining gas is separated from the fluid. After exit from the sponge material into cylindrical element located within a storage reservoir, the remaining gas rises to the chamber and passes through the hydrophobic membrane to the atmosphere.
Anther prior art filter, assigned to the assignee of the instant application, is disclosed in U.S. Pat. No. 4,900,308. There, the filter has a plenum sufficiently large so that the downward velocity of fluid is less than the upward velocity of gas bubbles that form in the fluid. A hydrophobic membrane covers the top of the plenum, so that, as the gas rises to the top of the plenum it is separated from the fluid and exits to the atmosphere through the hydrophobic membrane. This device relies on the phenomenon that the downward flow velocity for a fluid is less than the rate at which a bubble of gas to be removed will rise through the fluid. There is therefore no control with respect to the venting of the gas to atmosphere or the administration of the fluid to the patient. The disclosure of the '308 application is incorporated by reference herein.
Another gas elimination device, also assigned to the assignee of the instant application, is disclosed in U.S. Pat. No. 5,707,431. In the '431 gas elimination device, a cylindrical chamber is divided radially into two parts by a cylindrical filter centrally located within the chamber. A fluid inlet is located such that the input fluid is directed tangentially to the outer part of the chamber to create a vortex flow, which is stopped by passage of the fluid through the filter. The vortex motion causes the gas contained in the fluid to be separated from the fluid and rises to the top of the outer portion of the chamber. The top of the chamber is covered by a hydrophobic membrane, which allows the gas to exit the chamber to the atmosphere. A shut-off valve in the form of a float has a bottom end that engages the fluid output when there is adequate fluid present in the device. The '431 device therefore requires that a filter be used to divide radially into two parts a cylindrical chamber so that the gas in the fluid is removable therefrom. The disclosure of the '421 patent is incorporated by reference herein.